The invention relates to a device which utilizes a light-stimulable phosphor layer for recording and storing radiation images for readout at a later time. The phosphor layer has an energy gap between its conduction and valence bands. One or more defect energy levels are present in the energy gap. Electron/hole pairs are generated in the phosphor layer by exposing the layer to radiation in the image to be recorded. Some of these electrons or holes are trapped in the defect energy levels as they attempt to recombine. These trapped electrons or holes can be stimulated to recombine by exposing the phosphor layer to light. When the electrons or holes recombine, luminescent radiation is emitted by the phosphor, and the recorded image is read out.
U.S. Pat. No. 4,236,078 describes a method and device for recording and reproducing a radiation image which uses light-stimulable phosphors. The device includes a radiation source and a radiation image storage panel. The source irradiates an object to form a radiation image of the object on the panel. The radiation image is stored in the panel in the form of electrons or holes trapped in defect energy levels.
The radiation image storage panel is a phosphor layer which may be on a single transparent support base or sandwiched between two transparent support bases.
The image stored in the panel is read out by a light source such as a laser. The laser beam stimulates the panel to fluoresce. The intensity of the fluorescent light is proportional to the amount of radiation absorbed by the panel from the radiation image.
The fluorescent light emitted from the panel is passed to a photosensor. The photosensor generates an electrical signal proportional to the intensity of the fluorescent light. The signal is converted to an image by a reproduction device and a display device.
During readout of the stored image, a large part of the laser beam which is scanning the phosphor layer is reflected from the phosphor layer. This reflected laser light can be a source of noise if it is incident on the detector. Therefore, U.S. Pat. No. 4,236,078 provides a filter between the panel and the photosensor in order to remove any stray laser light which might be reflected off of the panel toward the photosensor.
Moreover, since a large part of the laser beam is reflected from the phosphor layer, less power is absorbed by the layer to stimulate luminescence. Therefore, either more powerful lasers must be used, or the phosphor layer must be scanned for a longer time in order to cause sufficient stimulated luminescence.